1. Field of the Invention
The present invention relates to a method and apparatus for generating synchrotron radiation, and a system involving such an apparatus.
2. Summary of the Prior Art
A storage ring is one example of a conventional synchrotron radiation generation apparatus (hereinafter SOR apparatus) for generating synchrotron radiation (hereinafter SOR radiation). In such a storage ring, a beam of charged particles such as electrons is caused to follow a looped path, under the influence of a series of bending magnets. Each bending magnet generates a bending magnetic field, which causes the beam to bend at that magnet. The path followed by the beam must be at very low pressure, and different types of vacuum pumps are used to achieve this. In the SOR apparatus described on pages 56 and 57 of the article "UVSOR Storage Ring", published by Science Research Institute (December 1982) the, deflection region where the beam of charged particles is bent does not have any vacuum pumps other than an ion pump. Other types of pumps which may be necessary, such as titanium pumps, are positioned between the bending magnets. This is because the conventional storage ring described in the above article is large, and there is plenty of space between the magnets for the pumps that are needed.
A further type of SOR apparatus is disclosed in EP-A-0278504 and corresponding U.S. Pat. No. 4,853,640. The SOR apparatus disclosed is generally similar to FIG. 1 of the accompanying drawings, in which the path of the electron beam comprises two straight regions 10, 11 extending generally parallel, with the ends of those straight regions 10,11 being joined by a semi-circular curved region 12,13. A single bending magnet 2 (FIG. 2) is provided adjacent to the semi-circular regions 12,13 respectively, to cause the beam to be bent through the corresponding semi-circle. Two inflectors 14,15 are provided along one of the straight regions 11, with one inflector 14 being connected via gate valves 16 to a turbo molecular pump 17. Further gate valves 18 and 19 are respectively connected to the two inflectors 14, 15. An RF cavity 20 is provided in the other of the straight regions 10 of the beam path, for accelerating the beam. Furthermore, at each point 21 along the path, there is provided a titanium getter pump and a turbo-molecular pump and at the points 22 are provided two titanium getter pumps.
In the SOR apparatus shown in FIG. 1, each semi-circular region 12,13 has four synchrotron radiation ducts 23 extending therefrom. When a beam of charged particles, such as electrons, is caused to move in a curved path, such as around the semi-circular regions 12,13, synchrotron radiation is generated and is caused to pass down the ducts 23.
In FIG. 2, a beam duct 1 is shaped to correspond to the semi-circular parts of the beam path 12,13 in FIG. 1. The core of a C-shaped bending electromagnet 2 surrounds the beam duct 1 so that the central axis of the beam duct 1 substantially corresponds to the center of the magnetic field generated by the bending magnet 2, with the bending electromagnet generating a leakage field 14.
An SOR radiation lead-out duct 3 corresponds to the ducts 23 in FIG. 1, and SOR radiation is emitted from windows 3a (FIG. 2) on the outer peripheral side of the beam duct 1, in the plane of the beam duct 1 and in a tangential direction. The outer edge of the lead-out duct 3 is sealed by a gate valve 5 and a seal flange 6 and is connected to a radiation beam line 7 which carries the synchrotron radiation beam to a user thereof.
An ion pump 4 is provided at the wall of the lead-out duct 3 between the outer frame of the core of the bending magnet 2 and the gate valve 5.
A standard ion pump has field generation means for generating a magnetic field therein, and in the conventional SOR apparatus, this field is aligned with the direction of elongation of the duct 3.